A typical data storage system includes data moving circuitry and an array of disk drives. Some data storage systems fit within standard-sized equipment cabinets or racks. The data moving circuitry for such data storage systems is typically fashioned into modules called blade servers, or simply blades, which are housed (perhaps in pairs) within enclosures. Such enclosures are commonly available in a variety of standard heights (e.g., 4U, 3U, 2U and 1U, where U is a standard measure of vertical height in the equipment cabinet and is equal to 1.75 inches in accordance with the EIA-310-D industry standard).
One conventional enclosure (hereinafter referred to as the conventional 4U enclosure) includes a 4U chassis, a midplane, two independent blades, two dual-port power supplies, and three pairs of fans. The midplane sits in the middle of the 4U chassis. The two blades independently plug into the midplane through a rear opening of the 4U chassis and reside in a stacked manner within the 4U chassis, one above the other. Similarly, the dual-port power supplies independently plug into the midplane through the rear opening of the 4U chassis and straddle the two blades along the sides of the 4U chassis. In particular, a rightside power supply sits right side up within the 4U chassis, and a leftside power supply sits upside down within the 4U chassis, thus enabling the manufacturer to connect both dual-port power supplies to the midplane while maintaining a single dual-port power supply design for the 4U chassis. One power cord to each dual port power supply plugs into the rear face of the power supply through an IEC-C14 appliance coupler mounted on each power supply. Additionally, each pair of fans plugs into the midplane through a front opening of the 4U chassis.
During operation, the midplane carries DC power supply signals from the two dual-port power supplies to the three pairs of fans and to the two blades (i.e., a first port of each dual-port power supply outputs power supply signals to one blade and a second port of each dual-port power supply outputs power supply signals to the other blade). The power for both the fans and the blades is diode-OR'd or shared to support backup of each other in the event of one DC power supply failing. Each blade of the 4U enclosure typically includes two microprocessors and performs data storage operations. For example, each blade stores data into and retrieves data from an adjacent array of disk drives on behalf of one or more external host computers. The three pairs of fans pass air over the blades in a shared configuration to thermally maintain the blades within a controlled temperature range.
If a component fails while the 4U enclosure is running, a technician typically can perform a hot swapping procedure to replace the failed component without completely powering down the 4U enclosure. For example, when the 4U enclosure loses a fan, the technician may need to replace a pair of fans having both the failed fan as well as an associated good fan thus placing the system into a further degraded mode until a repair is made. As a result, the 4U enclosure responds by transitioning from a normal operating mode in which the 4U enclosure performs data storage operations to a cache saving mode in which the 4U enclosure no longer performs data storage operations but instead writes the contents of cache memory out to the disk drive array. If the technician is successful in replacing the pair of fans within a two minute span (i.e., the length of operating time that can be sustained by its battery backup system), the 4U enclosure can transition back to the normal operating mode without ever shutting down completely. However, if the technician is unsuccessful in replacing the pair of fans within the two minute span, the 4U enclosure powers down safely and reliably so that no data is lost thus enabling the technician to restart the 4U enclosure at a later time.
Another conventional enclosure (hereinafter referred to as the conventional 1U enclosure) includes a 1U chassis, a single blade, two power supplies, two IEC-C14 appliance couplers, and an assembly of fans. Here, the single blade of the 1U enclosure includes two microprocessors, and resides on a motherboard which is rigidly fixed to the 1U chassis. If the blade fails, a technician simply replaces the entire 1U chassis.